Carbonic water is assumed to be effective for treatment of regressive diseases and peripheral circulatory disorders. For example, there is a method in which carbonic acid gas is fed in the form of bubbles into a bath (bubbling method), as a method of artificially producing carbonic water. However, the dissolving ratio is low, and the dissolution time is long in this method. Another method is a chemical method in which a carbonate salt is reacted with an acid (chemical method). However, it is necessary to add the chemical materials in large amounts, and it is impossible to keep a clearness in this method. Additionally, there is a method in which hot water and carbonic acid gas are sealed in a tank for a period of time while it is pressurized (pressure method). However, the size of the apparatus is increased impractically in this method.
Currently, commercially marketed apparatuses of producing carbonic water are used for producing carbonic water having a low concentration of carbonic acid gas which is about 100 to 140 mg/L. The apparatuses have no means of controlling the concentration of carbonic acid gas.
On the other hand, Japanese Patent Application Laid Open (JP-A) No. 2-279158 discloses a method in which a carbonic acid gas is fed through a hollow fiber semi-permeable membrane and absorbed by hot water. Further, JP-A No. 8-215270 discloses a method in which a pH sensor is put in a bath, and controls the feeding rate of carbonic acid gas into a carbonic acid gas dissolving apparatus for maintaining the concentration of the carbonic acid gas at a constant level in the water in the bath. Furthermore, International Publication No. 98/34579 pamphlet discloses a method in which concentration data for carbonic acid gas from the carbonic water produced is calculated from the pH value of carbonic water and the alkalinity of raw water. The feeding rate of carbonic acid gas is controlled so that the concentration of carbonic acid gas in carbonic water can reach its intended value. These are methods in which carbonic water is produced by passing once raw water through the carbonic acid gas dissolving apparatus that is equipped with a hollow membrane. The apparatus is called a one-pass type apparatus.
In the one-pass type apparatus, it is necessary to increase the membrane area of the hollow fiber membrane or to increase the pressure of carbonic acid gas in order to produce carbonic water having a high concentration which is excellent for physiological effects (e.g., blood flow increase). However, if the membrane area is increased, the size of the apparatus increases, and therefore it causes the cost to increase. Accordingly, if the pressure of gas is increased, the dissolving ratio becomes low. Furthermore, in the one-pass type apparatus, it is indispensable to have a pipe and a hose connection between the apparatus and hot water, such as tap water. As a result the connection must be re-set in every case that allows the apparatus to be moved for use anyplace.
On the other hand, carbonic water having a high concentration can be produced efficiently and at low cost by a so-called circulation type apparatus wherein hot water in a bath is circulated by a circulation pump through a carbonic acid gas dissolving apparatus. Additionally, the setting of the circulation type apparatus is very simple because it needs no additional connections, as is required in the one path type apparatus, but rather is completed by filling a bath with hot water and putting a carbonic water circulation hose from the apparatus into the bath. Examples of such circulation type carbonic water apparatuses include those disclosed by JP-A Nos. 8-215270 and 8-215271.
Under a condition in which carbonic water having a desired concentration of carbonic acid gas is filled in a bath, the carbonic acid gas in the carbonic water is evaporated, which results in gradually decreasing the concentration of carbonic acid gas. This tendency depends on the size of the bath. Particularly, when a large bath is filled with carbonic water for a large number of people, its evaporation rate is high, and the concentration of carbonic acid gas is quickly decreased. In a large bath for a large number of people, the hot water is often circulated through a filtration apparatus for cleaning the hot water even while the bath is being used. However, the carbonic acid gas evaporates in large amounts at the filtration apparatus if the carbonic water is contained in a circulation type bath in which the water is circulated through the filtration apparatus.
The method in which the feeding amount of carbonic acid gas is controlled based on the pH value, has a relatively large calculating error in determining the concentration of carbonic acid gas in the resulting carbonic water. Therefore, it is necessary to add an automatic correction factor to the pH sensor for suppressing the calculating error thereof within ±0.05. This requires complicated control techniques, increases the size of the apparatus and increases the cost. Additionally, the alkalinity of raw water (e.g., tap water) should be measured to control precisely the concentration of carbonic acid gas.
Examples of carbonic acid gas production apparatuses include so-called one-pass type apparatuses as disclosed in JP-A No. 2-279158, International Publication No. 98/34579 pamphlet in which carbonic water is produced by passing raw water once through a carbonic acid gas dissolving apparatus equipped with a hollow fiber membrane, and so-called circulation type apparatuses as disclosed in JP-A Nos. 8-215270 and 8-215271 in which hot water from a bath is circulated through a carbonic acid gas dissolving apparatus by a circulation pump. In any type apparatus, excess water collects at the outer parts of the hollow fiber membrane. The excess water permeates through the membrane from the hollow part of the hollow fiber membrane, or it is generated by the condensation of vapor which permeates through the membrane from the hollow part. When the excess water comes into contact with the surface of the membrane, the surface becomes clogged, and the gas permeation cannot be effectively performed. In conventional apparatuses, an operator appropriately opens a drain valve to discharge the excess water collected at the outside parts of the hollow fiber membrane.
It is conventionally known that a foot bath of carbonic water may improve the physiological functions of the foot. In a conventional foot bath, it is necessary that the foot bath is filled with carbonic water that was previously produced, or that the carbonic water was produced from hot water filled in the bath by using another apparatus. These operations are complicated to use. A portable type foot bath has merit in that the foot bath treatment can be conducted easily in any place, but the merit is restricted by the operations available for producing the carbonic water.